1. Field of the Invention
This invention relates to a non-autocrosslinking binder composition for water-dilutable lacquers, an aqueous electro-dip lacquer coating composition (KTL bath) capable of being deposited at the cathode and their use for coating articles.
2. Description of the Prior Art
Electro-dip lacquer coating compounds prepared on the basis of or using epoxide resins and capable of being deposited at the cathode are presently used on a large technical scale as electrophoresis lacquers or EC lacquers. They provide a high degree of throwing power and very high corrosion protection even on metal sheets which have not been phosphatized. Thermal crosslinking of these binders is carried out by various processes, e.g., by reactions with blocked polyisocyanates, by the addition of transesterifiable crosslinking agents or by the reaction of unsaturated double bonds (DE-A- 27 49 776; DE-A-34 36 345). Binders of this kind may give rise to surface defects such as pits which necessitate undesirable repair work in series lacquering. The properties of elasticity and resistance to stone chipping also require improvement.
Another class of materials of increasing importance are the KTL materials based on acrylate resins as described in DE-A-34 36 346. They are used on account of their low tendency to yellowing and high weathering resistance but do not attain the desired level of corrosion protection if the quality of phosphatization fluctuates.